In many applications, particularly medical laser applications, it is necessary to concentrate relatively high laser power onto a small area, e.g., for ablating or cutting tissue. This application of lasers requires that the laser source be of high brightness; that is, it must emit a high power beam of small area and small divergence. Brightness is directly proportional to the output power and inversely proportional to the source area and also to the solid angle of the light beam. (Brightness=power/(Source Area x Solid Angle)) It is therefore difficult to increase the brightness of a source by increasing the output power, since this also tends to increase the source area and/or the solid angle of the light beam such that the net effect on the brightness is relatively small. For example, suppose the object is to double the brightness of a particular laser that emits 1 watt of power into a certain solid angle. By simply taking another such laser and placing it adjacent the first, the result is two watts of power into essentially the same solid angle, but the total cross-sectional area of the new source is also twice as large such that the brightness of the combined source is essentially equal to the brightness of each separate laser (not double the brightness).
It has been proposed to use a plurality of laser diodes to provide a higher power laser diode light source from an optical fiber. An example of such a laser diode light source is disclosed in UK Patent Application GB 2256503A.
The prior art teaches to increase the brightness of a light source by using a polarized beam combiner on two beams of light of orthogonal polarizations from two laser diodes, thus combining the two beams into a single composite beam. The prior art further teaches to feed this composite beam into a fiber optic cable and then to bundle a group of these fiber optic cables to form a larger more powerful beam of light. This method suffers from a number of problems some of which include: the power output being limited by being able to combine only two laser diodes with each polarized beam combiner, and the multitude of polarized lasers and optics being very complex and expensive (this method requires a large number of beam combiner pairs to achieve a desired high power).
Thus there exists a need for a more efficient way to combine a plurality of laser diodes to form a relatively high brightness laser light source for performing medical laser applications.
It is thus an object of the present invention to provide a method of and an apparatus for generating a beam of bright light for medical laser applications.
It is another object of the present invention to provide a method of and an apparatus for generating a beam of bright light by efficiently combining a plurality of semiconductor lasers.
It is another object of the present invention to provide a method of and an apparatus for generating a beam of bright light by combining a plurality of semiconductor lasers of different frequencies.
It is yet another object of the present invention to provide a method of performing medical laser applications by generating a first laser beam of a first frequency, generating a second laser beam of a second frequency, combining the first and second laser beams into a composite laser beam then shining the composite laser beam into tissue.
Another object of the present invention is to provide an apparatus for generating a beam of bright light utilizing semiconductor lasers of different frequencies, bundles of optical fibers to form composite single frequency laser beams from the lasers of different frequencies respectively and frequency responsive optics for combining the composite laser beams of the different frequencies into a combined laser beam.